Thermal integrator



Aug. 23, 1955 w. G. WING 2,716,214

THERMAL INTEGRATOR Filed oct. 21, 1952 Myx L O 2 lu E@ 4l 4 7 E Q L) l qIE q Z l' g m .a5 I E [u lg l: l h Q l Y I E l l to 2L,

TMEE-r- ,4 INVENTOR W/L/s C7. l/V/NG ATTORNEY United States IPatentTHERMAL rNrEGnAToR Willis G. Wing, Roslyn Heights, N. Y., assigner toSperry Rand Corporation, a corporation of Delaware Application October21, 1952, Serial No. 315,885

4 Claims. (Cl. 323-52) This invention relates to integrators, and morepar- 1 ticularly, is concerned with a thermal time delay device forsecuring an approximation to the time integration of limited voltagesignals.

Servo mechanisms frequently employ an integrating loop to reduce longterm errors in the system. Various integrators have heretofore beenproposed having a long time constant. However, for averaging an inputsignal over periods of 20 seconds or longer, known integrating systems,such as rotary or other mechanical integrators, orresistance-capacitance integrators, frequently prove to be complicatedand expensive, or may be prohibitive in size for some applications.

Thermal time delay devices have been used for integrating voltagesignals over a long time interval. One such known device employsresistance elements which differentially heat associated coils of hightemperature coeicient resistance wire in response to an input signal,The resistance wire coils are in turn connected in a bridge circuit,producing an output signal when the bridge is unbalanced by unequalchanges in resistance of the coils with differential heating by theinput signal. Thus, when an input signal is applied to a thermalintegrator of this type, unequal heating of the coils results in agradual change in the balance of the output bridge, the initial rate ofchange being approximately proportional to the magnitude of the inputsignal.

However, such a known thermal integrating device is subject to theobjection that the close proximity between the coils and the resistanceelements necessary for good thermal coupling gives rise to substantialcapacitive coupling between the input and output circuits when theintegrator is used with signal carriers having frequencies of the orderof 400 cycles.

It is the general object of this invention to avoid and overcome theforegoing and other difficulties of and objections to prior artpractices by the provision of a thermal-type integrating apparatus whichis rugged and compact in construction, relatively simple and inexpensiveto build, and yet, reliable and foolproof in operation.

Another object of this invention is to provide means for producing anoutput voltage signal which changes in amplitude at a rate proportionalto the amplitude of an input voltage signal over a substantial timeinterval up to 20 seconds or longer.

Another object of this invention is the provision of a thermalintegrator which may be operated on either A.C. or D.-C. input signals.

Another object of this invention is to provide apparatus for producing atime delay by thermal means which is only moderately affected by changesin ambient temperature.

These, and other objects of the invention which will become apparent asthe description proceeds, are achieved by the provision of athermal-type integrator comprising a frame to which a pair of spacedparallel bimetal elements are each secured at one of their respectiveends. A spacer bar having low thermal conductivity is secured to andbetween the opposite ends of the bimetal elements. The bimetal elementsare so arranged that they tend to bend toward or away from each otherwith similar changes in temperature so that only unequal heating andcooling of the bimetal elements results in lateral movement of thespacer bar. Electrical heating means, associated with each of thebimetal elements, dilerentially heat the elements in response to aninput signal to the thermal integrator, the unequal heating of theelements effecting a net lateral movement of the spacer bar at a ratedetermined by the magnitude of the input signal. An E-transformerpick-olf is supported by the frame and connected to the spacer bar insuch manner that the movement of the spacer bar with unequal heating ofthe bimetal elements actuates the pick-off to produce an output signalof amplitude substantially proportional to the deection of the pick-ofi.

For a better understanding of the invention, reference should be had tothe accompanying drawing, wherein:

Fig. 1 is a plan View of the thermal integrator showing the electricalconnections thereto;

Fig. 2 is a sectional view of the thermal integrator taken substantiallyon the line lI-ll of Fig. l; and

Fig. 3 is a graphical representation of the output signal of the thermalintegrator as a function of time following application of a constantinput signal.

With specic reference to the form of the invention as illustrated in thedrawing, the numeral 10 indicates generally a base to which is securedby a suitable means, such as screws l2, an angle bracket 14. The anglebracket 14 has secured thereto a spacer bar 16, which is preferably madeof a low thermal conductivity material such as stainless steel. Thespacer bar 16 is adjustably secured to the angle bracket t4 by means ofthe screws 18 and 2t) which pass through longitudinal slots 22 and 24respectively in the spacer bracket 16 and threadedly engage the anglebracket lll. The slots 22 and 24 permit lateral adjustment of the spacerbar 16 relative to the base llt).

Secured to each end of the spacer bar 16 are a pair of bimetal elements26 and 28 which are of a reverse welded type that bends in an S-shapewhen heated. Each bimetal element is actually made of two sections ofbimetal welded end to end, each section bending the opposite directionfrom the other with a change in temperature. The bimetal elements aresuitably secured to the spacer bar, as by screws 30.

The opposite ends of the bimetal elements are secured to a second spacerbar 34 by suitable means, such as screws 36. The bimetal elements 26 and28 act as cantilever supports for the spacer bar 34, bending of eitherof the bimetal elements producing lateral movement of the spacer bar 34.

Wound around each of the bimetal elements 26 and 28 are coils 38 and 40respectively, the coils being wound with suitable resistance wire sothat current passing through the coils generates heat which istransferred to the bimetal elements 26 and 28. Electrical insulation inthe form of a coating or sleeving 4l on both the bimetal elementsprevents electrical short circuiting between the individual turns of thecoils and between the coils and the bimetal elements.

The coils 38 and 40 are electrically connected in series at a commonjunction 42. The other end of the coil 38 is connected to a referencevoltage source supplying a voltage er, while the other end of the coil4t) is connected to a second reference voltage source supplying avoltage e2. To elect heating of the coils 38 and 40, the referencevoltages e1 and e2 may be either alternating current or direct currentsignals.

If e1 and e2 are alternating current reference signals, they must be ofopposite phase and equal amplitude to provide equal heating of the coils3S and 40 with the common junction 42 being at Zero potential. Forexample, a suitable source for e1 and e2 would be a centertappedtransformer. lf direct current reference Voltage signals are used, theymust be of equal potentials and opposite polarities to give equalheating of the coils 33 and 4t) with the common junction 42 at zeropotential.

An input signal ein is applied at the common junction 42. lf the inputsignal is in phase with e1 and out of phase with ez (or of the samepolarity as ci and opposite polarity from e2 where direct currentsignals are used) the coil 4@ is heated more than the coil 3S, resultingin unequal bending stresses in the bimetal elements 26 and 2S and alateral displacement of the spacer bar 34. The bimetal elements aremounted to act in opposition to each other, so that a net lateralmovement of the spacer bar 34 is effected in the direction of bending ofthe hotter bimetal element.

lf the phase of the input signal is reversed, the coil 3S is heated upmore than coil 4t), resulting in a net lateral displacement of thespacer bar 34 in the opposite direction. The extent of the movement ofthe spacer bar 34 depends on the difference in temperature between thebimetal element 26 and the bimetal element 28.

Referring to Fig. 3, motion of the spacer bar 34 resulting from constantinput signals of selected amplitudes are plotted as a function of time.Curve 45 is for a small input signal ein, and curves 47 and 49 are forrespectively higher amplitudes of input signals. During the interval tto t1, the slopes of the respective curves are substantially straightand at different slopes which correspond to the different input signals.Thus, over the region to to li, the rate of movement of the spacer baris substantially constant and varies directly with the magnitude of theinput signal. By providing means for detecting movement of the spacerbar, an output signal can be produced which approximates the timeintegral of the input signal, that is, an output signal which changes ata rate substantially proportional to the instantaneous magnitude of theinput signal.

Motion of the spacer bar 34 is preferably detected by means of anE-transformer type pick-ntf, indicated generally at 48. The magneticcircuit of the E-transformer includes three arms t), 52 and 54 joined bya common bar 56. A pair of outer coils 58 and 60 are wound on the armsSti and 54 and are connected in series at 62. An exciting coil 64,connected across a source of alternating current, is wound around thecenter arm 52.

The outer arms 5t] and 54 are bridged by a jumper bar 65 which has aprojection 66 at the middle thereof forming a magnetic gap 68 with thecenter arm 52. The whole E-transformer assembly is held together andsupported from the bracket 14 by a clamping bar 70 secured in positionby bolts 71.

Secured to the spacer bar 34 and passing through the gap 68 is a lowresistance shorted turn including a U- shaped copper member 72 andbridging copper bar 74 soldered across the ends of the U-shaped member72 and extending through the gap 68. When the shorted turn is centeredin the gap 68, flux produced by energization of the exciting coil 64splits and passes equally between the two coils 50 and 52. No net outputsignal is produced at terminals eout since the coils 5t) and 52 areconnected so as to oppose each other. Movement of the spacer bar 34either to the right or to the left unbalances the flux paths between thetwo coils 50 and 52, to produce a net output signal whose phase dependsupon the direction in which the spacer bar 34 is moved. Strips of iron,indicated at 76, secured along the edges of the bridging bar '7 4,reduces the effective air gap for the portion of the ux that splitsaround the shorted turn.

By moving a shorted secondary coil rather than an armature, as in theconventional E-transformer, slight transverse movement of the spacer bar34, which necessarily accompanies the lateral movement thereof, does notaffect the balance or sensitivity of the pick-off.

The E-transformer is set to provide Zero output signal with nointegrator input signal ein by adjusting the spacer bar 16 so that theshorted turn is positioned in the center of the gap 6E. Since thelimited elements oppose each other in bending with changes intemperature, the ambient temperature does not affect the Zero setting,changes in the ambient temperature acting equally on the two elementsand thereby being cancelled out.

From the above description, it will be recognized that the variousobjects of the invention have been achieved with the provision of anintegrator which is relatively simple in construction and design. Thelong time delay between the input and output signals provides anapproximate time integration of either A.C. or D.C. input signals and isparticularly adapted for use in servomotor control systems where asmoothing effect is required. The sensitivity and gain of the integratorare good, and the construction provides complete isolation between theoutput and input circuits.

Since many changes could be made in the above construction and manyapparently Widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A thermal integrator comprising a frame, a pair of spaced parallelreverse welded bimetal elements, each of the bimetal elements beingsecured at one end thereof to the frame, a spacer bar having a lowcoefficient of thermal conductivity secured to and between the oppositeends of the bimetal elements, the bimetal elements being mounted to bendin opposite directions with respect to each other when heated,electrical heating coils extending around each of the bimetal elementsand connected in series across a source of potential, the input signalto the integrator being connected to the common junction between theheating coils, an E-transformer supported by the frame and having an airgap in the center leg thereof, and a shorted turn of conductive materialsupported by the spacer bar and extending through the air gap, theE-transformer producing an output signal in response to changes inposition of the shorted turn in the air gap with movement of the spacerbar.

2. A thermal integrator for producing an output signal that is asmoothed version of an input signal of changing amplitude, theintegrator comprising a frame, a pair of spaced parallel reverse Weldedbimetal elements, each of the bimetal elements being secured at one endthereof to the frame, a spacer bar having a low coecient of thermalconductivity secured to and between the opposite ends of the bimetalelements, the bimetal elements being mounted to bend in oppositedirections with respect to each other when heated, electrical heatingcoils extending around each of the bimetal elements and connected inseries across a voltage source, the input signal to the integrator beingconnected to the common junction between the heating coils, anE-transforrner supported by the frame including an armature connected tothe spacer bar, the E-transformer when energized by an A.C. sourceproducing an output signal having an amplitude which is varied inresponse to changes in position of the spacer bar.

3. A thermal integrator comprising a frame, a pair of `spaced parallelreverse welded type bimetal elements, each or" the bimetal elementsbeing rigidly secured at one end thereof to the frame, a spacer barhaving a low coefficient of thermal conductivity rigidly secured to andbetween the opposite ends of the bimetal elements, the bimetal elementsbeing mounted to bend in opposite directions with respect to each otherwhen heated, electrical heating coils extending around each of thebimetal elements and connected in series across a source of potential,the input signal to the integrator being connected to the commonjunction between the heating coils, and means supported by the frame andconnected to the spacer bar for producing an output signal having anamplitude which is varied n response to changes in position of thespacer bar.

4. A thermal integrator for producing an output signal that is asmoothed version of an input signal of varying amplitude, saidintegrator comprising a pair of thermomechanical elements adapted tochange their physical dimensions when heated, first electrical heatingmeans associated with one of said elements, second electrical heatingmeans associated with the other of said elements, the input signal beingconnected in series With said first means and a rst voltage source, theinput .signal further being connected in series with said second meansand a second voltage source, whereby said thermomechanical elements areheated differentially in response to varia- 15 tions in amplitude of theinput signal, the rate of heating and cooling of said thermomechanicalelements in respense to said first and second heating means being slowcompared to the normal rate of change in amplitude of said input signal,and means operatively associated with said thermomechanical elements andmovable under the joint influence thereof, said last-named meansproducing an output signal that varies in amplitude in proportion to thenet movement thereof by said thermomechanical 10 elements.

References Cited in the file of this patent UNITED STATES PATENTS1,886,439 Wells Nov. 8, 1932

